The PI will continue to determine the effects of dietary-induced zinc deficiency on ocular tissue, liver and plasma. Light and electron microscopic studies will be correlated with biochemical data. Weanling and adult rats will be used. The severity of zinc deficiency will be assessed by determining zinc levels in the femurs of zinc-deficient (ZD), pair-fed (PF), and ad libitum (AL) controls by means of atomic absorption spectrophotometry at various intervals. The role of zinc in the maintenance of normal retinal pigment epithelial cell metabolism and its relationship to the viability of the photoreceptor is being investigated. We will examine the interaction between zinc and vitamin A in the eye and liver of the animal groups mentioned above. Identification and retinoids in the eye and liver of ZD compared to the controls will be performed. It is reported that zinc affects the synthesis and transport of serum retinol-binding protein (SRBP). Circulating levels of vitamin A will be determined by HPLC. Plasma levels of transthyretin (TTR), which complexes with SRBP and retinol for transport of vitamin A to the eye, will be determined by crossed immunoelectrophoresis. Isolation and purification of SRBP will be done by affinity column chromatography. The purified SRBP will be used for the production of antibodies, which will permit quantitation of the rate of synthesis and release of TTR and SRBP by perfused liver preparations. Retinoid content of the eyes of ZD, PF and AL rats under the conditions of light and dark adaptation will be measured by HPLC. Rhodopsin will be measured from the absorbance loss at 498 nm before and after bleaching. The presence of interstitial retinol-binding protein (IRBP), a carrier protein which may be involved in the transport of retinoids between rod outer segments and RPE, will be ascertained in the three groups of animals at varying time periods by SDS-polyacrylamide gel chromatography. We will also determine whether there is a change in all-trans retinol dehydrogenase in rod outer segments. A related project will study the effect of the iron chelator, deferoxamine, on the morphology of the RPE which is similar to that observed in ZD rats. Visual function (ERG), followed by preparation of rod outer segments for determination of levels of polyunsaturated fatty acid and lipid peroxides, will be studied. Biochemical identification and characterization of the inclusion bodies seen in the RPE of zinc-deficient and deferoxamine-treated rats will also be performed.